Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$54.43	9.800%	$59.7641	$59.76	$59.75	$59.80
Purchase #2	$42.83	3.757%	$44.4391	$44.44	$44.45	$44.40
Purchase #3	$129.72	10.563%	$143.4223	$143.42	$143.40	$143.40
Purchase #4	$207.98	10.353%	$229.5122	$229.51	$229.50	$229.50
Purchase #5	$163.81	12.697%	$184.609	$184.61	$184.60	$184.60
Purchase #6	$114.83	4.583%	$120.0927	$120.09	$120.10	$120.10
Purchase #7	$77.44	8.279%	$83.8513	$83.85	$83.85	$83.90
7 purchase totals =	$791.04		$865.6907	$865.68	$865.65	$865.70